1. Field of the Invention
The present invention relates to a technique by which a display panel which is flexible (having a flexibility) is provided, and more particularly to a technique by which a flexible active matrix liquid-crystal display unit is provided.
2. Description of the Related Art
There has been known a liquid-crystal display unit as a display unit which is small-sized, light in weight and of the thin type. This has a structure in which liquid crystal is interposed between a pair of translucent substrates which are bonded to each other at intervals of several xcexcm and held in this state as the structure of a display panel. In the operation of the display unit, an electric field is applied to liquid crystal in a predetermined region so as to change its optical characteristics, whereby the presence/absence of a light transmitted through a panel and the amount of transmitted light are controlled.
As a technique by which the display characteristics of this liquid-crystal display unit is further enhanced, there has been known the active matrix display panel. This is to arrange switching thin-film transistors (in general, an amorphous silicon thin film is used) in the respective pixels disposed in the form of a matrix, and to control charges that takes in or out of the respective pixels by the thin-film transistors.
In order to improve the characteristics of the active matrix liquid-crystal display device, it is necessary to improve the characteristics of the thin-film transistor as used. However, under the existing circumstance, it is difficult to improve such characteristics in view of the relationship of the substrate as used.
What is required for the substrate used in the liquid-crystal display panel is such an optical characteristic that the substrate transmits a visible light. Substrates having such an optical characteristic are of a variety of resin substrates, a glass substrate, a quartz substrate, etc. Of them, the resin substrate is low in a heat-resistance, and therefore it is hard to manufacture the thin-film transistor on its surface. Also, the quartz substrate can withstand a high temperature of 1000xc2x0 C. or more, however, it is expensive and causes an economical problem when the display unit is enlarged. For that reason, the glass substrate is generally used.
In order to improve the characteristics of the thin-film transistor, a silicon semiconductor thin film having a crystalline property need be used for the thin-film semiconductor that forms the thin-film transistor. However, in order to form the crystalline silicon thin film, a sample must be exposed to a high-temperature atmosphere, and in the case of using the glass substrate, there arises such a problem that the substrate is warped or deformed. In particular, when making the substrate large in area, that problem becomes remarkable.
As a technique by which a liquid-crystal display panel that solves such a problem and has a high display characteristic is obtained, there has been known a technique disclosed in Japanese Patent Unexamined Publication No. Hei 6-504139. This technique is that a thin-film transistor is manufactured by using a monocrystal silicon thin film formed through the SOI technique, etc., that thin-film transistor is peeled off from the substrate for an epitaxial growth, and the thin-film transistor is bonded to an arbitrary substrate having an optical characteristic as required, to thereby obtain a panel constituting a liquid-crystal display unit.
In the case of using this technique, since the monocrystal silicon thin film formed using a known SOI technique can be used, a thin-film transistor having a high characteristic can be obtained. Also, a substrate having a curved surface can be used.
In the technique disclosed in Japanese Patent Unexamined Publication No. Hei 6-504139, a thin-film transistor is manufactured using the SOI technique. However, in the SOI technique under the existing circumstance, it is difficult to form a monocrystal thin film in a large area of 10 inch diagonal or more.
For example, under the existing circumstance, the maximum monocrystal wafer is of 16 inches in size. In this case, the maximum square panel as obtained is of 16xc3x97(xc2xd)xe2x88x922≈11 inch diagonal.
On the other hand, it is expected that the liquid-crystal display panel as required is of 20 or 30 inches or more in the diagonal dimension in the future. It is impossible to constitute such a large-sized liquid-crystal display panel through the method using the known SOI technique.
The present invention has been made in view of the above, and an object of the present invention is to provide a technique by which a thin-film transistor having a high characteristic over a large area is manufactured.
Another object of the present invention is to provide a technique by which a display panel is obtained using that technique.
Still another object of the present invention is to provide a thin-film transistor and a display panel which are manufactured using the above-mentioned techniques.
In order to solve the above-mentioned problems, one aspect of the present invention has been achieved by the provision of a method of manufacturing a semiconductor device, comprising the steps of:
forming a first insulating film on a first substrate;
forming a second insulating film on the first insulating film;
forming an amorphous silicon film on said second insulating film;
holding a metal element that promotes the crystallization of silicon in contact with a surface of said amorphous silicon film;
crystallizing said amorphous silicon film through a heat treatment to obtain a crystalline silicon film;
forming a thin-film transistor using said crystalline silicon film;
forming a sealing layer that seals said thin-film transistor;
bonding a second substrate having a translucent property to said sealing layer; and
removing said first insulating film to peel off said first substrate.
A specified example of the above-mentioned structure is shown in FIGS. 1 to 3. First, in FIG. 1, a first insulating film (silicon oxide film) 102 that functions as a peeling layer is formed on a glass substrate 101 which forms a first substrate. Then, a silicon oxide film 103 is formed as a second insulating film. The silicon oxide films 102 and 103 are manufactured by different methods, respectively, and the first silicon oxide film 102 is made of a material which is readily removed by etching at a poststage.
Subsequently, an amorphous silicon film 104 is formed on a second insulating film 103. Then, a solvent containing a metal element that promotes the crystallization of silicon therein is coated on the amorphous silicon film 104, to thereby form a water film 105, and a spin dry process is conducted using a spinner 106 into a state in which the metal element is brought in contact with the surface of the amorphous silicon film 104.
Thereafter, a crystal silicon film 107 is obtained by conducting a heat treatment, and the crystalline silicon film 107 is formed into an active layer 108, to thereby form a thin-film transistor as shown in FIGS. 2A and 2B. After the formation of the thin-film transistor, a layer 119 for sealing the thin-film transistor is formed. Then, a flexible translucent substrate 120 is bonded onto the layer 119. Thereafter, the silicon oxide film which is of the first insulating film 102 forming a peeling layer is removed by conducting an etching process so that the glass substrate 101 is peeled off from the thin-film transistor.
Another aspect of the present invention has been achieved by the provision of a method of manufacturing a semiconductor device, which comprises the steps of:
forming a first insulating film on a first substrate having a groove formed in a surface thereof;
forming a second insulating film on said first insulating film;
forming an amorphous silicon film on said second insulating film;
holding a metal element that promotes the crystallization of silicon in contact with a surface of said amorphous silicon film;
crystallizing said amorphous silicon film through a heat treatment to obtain a crystalline silicon film;
forming a thin-film transistor using said crystalline silicon film;
forming a sealing layer that seals said thin-film transistor;
bonding a second substrate having a translucent property to said sealing layer; and
removing said first insulating film by using an etching solvent to peel off said first substrate.
Still another aspect of the present invention has been achieved by the provision of a method of manufacturing a semiconductor device, which comprises the steps of:
forming a first insulating film on a first substrate having a groove formed in a surface thereof;
forming a second insulating film on said first insulating film;
forming an amorphous silicon film on said second insulating film;
holding a metal element that promotes the crystallization of silicon in contact with a surface of said amorphous silicon film;
crystallizing said amorphous silicon film through a heat treatment to obtain a crystalline silicon film;
forming a thin-film transistor using said crystalline silicon film;
forming a sealing layer that seals said thin-film transistor;
bonding a second substrate having a translucent property to said sealing layer; and
removing said first insulating film by using an etching solvent to peel off said first substrate;
wherein a gap is defined between a bottom portion of said groove and said insulating film, and said etching solvent enters said gap.
In the structures described in this specification, one kind or plural kinds of elements selected from Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu and Au can be used for the metal element that promotes the crystallization of silicon. In particular, Ni can obtain the higher reproducibility and effects.
Also, the metal element that promotes the crystallization of silicon is so adjusted as to provide a density of 1xc3x971014 to 5xc3x971018 atm cmxe2x88x923 in the silicon film. This is because the density of 1xc3x971014 atms cmxe2x88x923 is required for crystallization, and the density of more than 5xc3x971018 atm cmxe2x88x923 causes the semiconductor characteristic to be lowered. It should be noted that the density of atoms is defined as a maximum value of values measured by using SIMS (secondary ion mass spectroscopy) in this specification.
The crystalline silicon film obtained by using the above-mentioned metal element contains hydrogen and/or halogen at the density of 0.0005 to 5 atms % for neutralization of an unpaired coupling therein. Examples of the halogen are chlorine, fluorine and bromine.
Yet still another aspect of the present invention has been achieved by the provision of a method of manufacturing a semiconductor device, which comprises the steps of:
forming a first insulating film on a first substrate;
forming a second insulating film on said first insulating film;
forming an amorphous silicon film on said second insulating film;
holding a metal element that promotes the crystallization of silicon in contact with a surface of said amorphous silicon film;
irradiating a laser beam onto said amorphous silicon film to change a region on which the laser beam is irradiated into a monocrystal-like region or substantially monocrystal-like region;
forming a thin-film transistor by using the monocrystal-like region or substantially monocrystal-like region as an active layer;
forming a sealing layer that seals said thin-film transistor;
bonding a second substrate having a translucent property to said sealing layer; and
removing said first insulating film to peel off said first substrate.
In the above-mentioned structure, the monocrystal-like region or substantially monocrystal-like region contains substantially no grain boundary therein, contains hydrogen and/or halogen atoms for compensating a defect at a density of 1xc3x971015 to 1xc3x971020 atms cmxe2x88x923 therein, also contains carbon and nitrogen atoms at a density of 1xc3x971016 to 5xc3x971018 atms cmxe2x88x923, and further contains oxygen atoms at a density of 1xc3x971017 to 5xc3x971019 atms cmxe2x88x923.
Yet still another aspect of the present invention has been achieved by the provision of a method of manufacturing a semiconductor device, comprising the steps of:
forming a first insulating film on a first substrate;
forming a second insulating film on said first insulating film;
forming an amorphous silicon film on said second insulating film;
holding a metal element that promotes the crystallization of silicon in contact with a surface of said amorphous silicon film;
irradiating a laser beam onto said amorphous silicon film to change a region on which the laser beam is irradiated into a region having a crystalline property;
forming a thin-film transistor by using the region having the crystalline property as an active layer;
forming a sealing layer that seals said thin-film transistor;
bonding a second substrate having a translucent property to said sealing layer; and
removing said first insulating film to peel off said first substrate.
In a method of introducing the metal element that promotes the crystallization of silicon in accordance with the present invention described in this specification, it is simple to use a solvent containing the metal element therein. For example, in the case of using Ni, at least one kind of compound selected from nickel bromide solvent, nickel acetate solvent, nickel oxalate solvent, nickel carbonate solvent, nickel chloride solvent, nickel iodide solvent, nickel nitrate solvent, nickel sulfate solvent, nickel formate solvent, nickel acetylacenate solvent, nickel 4-cyclohexyl butyrate solvent, nickel 2-ethyl hexanoic acid solvent, nickel oxide solvent, and nickel hydroxide solvent can be used.
In the case of using Fe (iron) as the metal element, a material known as ion salt, for example, an Fe compound selected from bromide (FeBr26H2O), iron (II) bromide (FeBr36H2O), iron (II) acetate (Fe(C2H3O2)3xH2O), iron (I) chloride (FeCl24H2O), iron (II) chloride (FeCl36H2O), iron (II) fluoride (FeF33H2O), iron (II) nitrate (Fe(NO3)9H2O), iron (I) phosphorate (Fe3(PO4)28H2O), and iron (II) phosphorate (FePO42H2O) can be used.
In the case of using Co (cobalt) as the metal element, a material known as a cobalt salt, a Co compound selected from a material known as a cobalt salt, for example, cobalt bromide (CoBr6 H2O), cobalt acetate (Co(C2H3O2)24H2O), cobalt chloride (CoCl26H2O), cobalt fluoride (CoF2 xH2O), and cobalt nitrate (Co(No3)26H2O) can be used.
In the case of using Ru (ruthenium) as the metal element, as a ruthenium compound, a material known as ruthenium salt, for example, ruthenium chloride (RuCl3H2O) can be used.
In the case of using Rh (rhodium) as the metal compound, as a rhodium compound, a material known as rhodium salt, for example, rhodium chloride (RhCl33H2O) can be used.
In the case of using Pd (palladium) as the metal element, as a palladium compound, a material known as palladium salt, for example, palladium chloride (PdCl22H2O) can be used.
In the case of using Os (osmium) as the metal element, as an osmium compound, a material known as osmium salt, for example, osmium chloride (OsCl3) can be used.
In the case of using Ir (iridium) as the metal element, as an iridium compound, a material known as iridium salt, for example, a material selected from iridium trichloride (IrCl33H2O) and indium tetrachloride (IrCl4) can be used.
In the case of using Pt (platinum) as the metal element, as a platinum compound, a material known as platinum salt, for example, platinum (II) chloride (PtCl45H2O) can be used.
In the case of using Cu (copper) as the metal element, as a copper compound, a material selected from copper (II) acetate (Cu(CH3COO)2), copper (II) chloride (CuCl22H2O) and copper (II) nitrate (Cu(NO3)23H2O) can be used.
In the case of using gold as the metal element, as a gold compound, a material selected from gold trichloride (AuCl3 xh2O) and gold nitride (AuHCl44H2O) can be used.